Producing STTD diversity signal from rake combined level 3 message

ABSTRACT

A circuit is designed with a measurement circuit ( 746 ) coupled to receive an input signal from at least one of a first antenna and a second antenna of a transmitter. The measurement circuit produces an output signal corresponding to a magnitude of the input signal. A control circuit ( 726 ) is coupled to receive the output signal, a first reference signal (.eta..sub.1) and a second reference signal (.eta..sub.2). The control circuit is arranged to produce a control signal in response to a comparison of the output signal, the first reference signal and the second reference signal.

This application is a divisional of application Ser. No. 10/808,621,filed Mar. 24, 2004, now U.S. Pat. No. 7,555,068, issued Jun. 30, 2009;

Which is a divisional of application Ser. No. 09/373,855, filed Aug. 13,1999, now U.S. Pat. No. 6,728,302, granted Apr. 27, 2004. Which claimspriority under 35 U.S.C. .sctn. 119(e)(1) of provisional application No.60/119,732, filed Feb. 12, 1999 and provisional application No.60/120,609, filed Feb. 18, 1999.

FIELD OF THE INVENTION

This invention relates to wideband code division multiple access (WCDMA)for a communication system and more particularly to space-time transmitdiversity (STTD) detection for WCDMA signals.

BACKGROUND OF THE INVENTION

Present code division multiple access (CDMA) systems are characterizedby simultaneous transmission of different data signals over a commonchannel by assigning each signal a unique code. This unique code ismatched with a code of a selected receiver to determine the properrecipient of a data signal. These different data signals arrive at thereceiver via multiple paths due to ground clutter and unpredictablesignal reflection. Additive effects of these multiple data signals atthe receiver may result in significant fading or variation in receivedsignal strength. In general, this fading due to multiple data paths maybe diminished by spreading the transmitted energy over a wide bandwidth.This wide bandwidth results in greatly reduced fading compared to narrowband transmission modes such as frequency division multiple access(FDMA) or time division multiple access (TDMA).

Previous studies have shown that multiple transmit antennas may improvereception by increasing transmit diversity for narrow band communicationsystems. In their paper New Detection Schemes for Transmit Diversitywith no Channel Estimation, Tarokh et al. describe such a transmitdiversity scheme for a TDMA system. The same concept is described in ASimple Transmitter Diversity Technique for Wireless Communications byAlamouti. Tarokh et al. and Alamouti, however, fail to teach such atransmit diversity scheme for a WCDMA communication system.

New standards are continually emerging for transmit diversity of nextgeneration wideband code division multiple access (WCDMA) communicationsystems as described in Provisional U.S. Patent Application No.60/116,268, filed Jan. 19, 1999, and incorporated herein by reference.These WCDMA systems are coherent communications systems with pilotsymbol assisted channel estimation schemes. These pilot symbols aretransmitted as quadrature phase shift keyed (QPSK) known data inpredetermined time frames to any receivers within range. The frames maypropagate in a discontinuous transmission (DTX) mode. For voice traffic,transmission of user data occurs when the user speaks, but no datasymbol transmission occurs when the user is silent. Similarly for packetdata, the user data may be transmitted only when packets are ready to besent. The frames are subdivided into sixteen equal time slots of 0.625milliseconds each. Each time slot is further subdivided into equalsymbol times. At a data rate of 32 KSPS, for example, each time slotincludes twenty symbol times. Each frame includes pilot symbols as wellas other control symbols such as transmit power control (TPC) symbolsand rate information (RI) symbols. These control symbols includemultiple bits otherwise known as chips to distinguish them from databits. The chip transmission time (T_(C)), therefore, is equal to thesymbol time rate (T) divided by the number of chips in the symbol (N).

A mobile unit must initially receive and synchronize with data framestransmitted by one or more remote base stations. Each base stationcontinually transmits broadcast channel (BCH) data over the primarycommon control physical channel (PCCPCH) to identify itself to mobileunits within the cell. Referring to FIG. 1, there is a simplified blockdiagram of a typical diversity transmitter of the prior art. Thetransmitter simultaneously transmits primary and secondarysynchronization codes on respective primary (P-SCH) 150 and secondary(S-SCH) 160 channels to uniquely identify each base station signalreceived by the mobile unit. Circuits 156 and 166 modulate the gain ofthese synchronization codes in response to respective gain factorsGP-SCH on lead 154 and GP-SCH on lead 164. Circuit 170 adds thesynchronization codes and applies them to time switch (TSW) 174 via lead172. Time switch 174 selectively applies the synchronization codes toswitches SW0 134 and SW1 136 in response to the control signal at lead140 as indicated by inset 190. These P-SCH and S-SCH codes aretransmitted as symbol 300 (FIG. 3) in time slot 1.

Broadcast channel data (BCH) for the PCCPCH are applied to channelencoder 108 via lead 106 (FIG. 1). Interleaver circuit 110 applies theBCH data to space-time transmit diversity (STTD) encoder circuit 112.The STTD encoder produces encoded output data at lead 114 for thetransmit antenna (Ant 1) and at lead 116 for the diversity antenna (Ant2). Multiplex circuit 118 produces this STTD encoded BCH data on leads120 and 122 at a time corresponding to data symbols 302 of time slot 1(FIG. 3). The BCH data are modulated by spreading and scrambling codeson lead 124 and applied to switches SW0 134 and SW1 136. These switchesSW0 and SW1 selectively multiplex SCH data with BCH data and pilotsymbols in response to a control signal on lead 138 as shown at inset190. The BCH data at lead 180 are then applied to the transmit antenna(Ant 1), and the data at lead 182 is applied to the diversity antenna(Ant 2).

Pilot symbol data for the PCCPCH are applied to lead 100. Diversitycircuit 102 generates an open loop transmit diversity (OTD) symbolpattern at lead 104 for the diversity antenna. This OTD pattern togetherwith the pilot symbol pattern for the transmit antenna is shown at TABLEI for each of the sixteen time slots in a frame. By way of comparison,the STTD pilot symbol pattern for diversity antenna (Ant 2) transmissionon the dedicated physical data channel (DPDCH) is also shown. The pilotsymbols at leads 100 and 102 are applied to multiplex circuit 118.Multiplex circuit 118 selectively applies the pilot symbols at leads 100and 102 to leads 120 and 122, respectively, at a time corresponding topilot symbols 304 of time slot 1 (FIG. 3). Thus, multiplex circuit 118multiplexes STTD encoded data symbols 302 with OTD encoded pilot symbols304. The pilot symbols at leads 120 and 122 are then modulated withspreading and scrambling code. These modulated pilot symbols at leads130 and 132 are further multiplexed with SCH data by switches 134 and136, respectively, in response to the control signal at lead 138 asshown at inset 190. The resulting pilot symbols are applied to transmitand diversity antennas via leads 180 and 182, respectively.

TABLE 1 TRANSMIT ANTENNA STTD ANT 2 OTD ANT 2 SLOT B₁ S₁ B₂ S₂ B₁ −S₂*−B₂ S₁* B₁ S₁ −B₂ −S₂ 1 11 11 11 11 11 01 00 10 11 11 00 00 2 11 11 1101 11 11 00 10 11 11 00 10 3 11 01 11 01 11 11 00 00 11 01 00 10 4 11 1011 01 11 11 00 11 11 10 00 10 5 11 10 11 11 11 01 00 11 11 10 00 00 6 1110 11 11 11 01 00 11 11 10 00 00 7 11 01 11 00 11 10 00 00 11 01 00 11 811 10 11 01 11 11 00 11 11 10 00 10 9 11 11 11 00 11 10 00 10 11 11 0011 10 11 01 11 01 11 11 00 00 11 01 00 10 11 11 11 11 10 11 00 00 10 1111 00 01 12 11 01 11 01 11 11 00 00 11 01 00 10 13 11 00 11 01 11 11 0001 11 00 00 10 14 11 10 11 00 11 10 00 11 11 10 00 11 15 11 01 11 00 1110 00 00 11 01 00 11 16 11 00 11 00 11 10 00 01 11 00 00 11

Turning now to FIG. 2, there is a block diagram showing signal flow inan OTD encoder 102 of the prior art for pilot symbol encoding of thetransmitter of FIG. 1. The pilot symbols are predetermined controlsignals that may be used for channel estimation and other functions aswill be described in detail. The OTD encoder 102 receives pilot symbolsB₁, S₁, B₂ and S₂ at symbol times T-4T, respectively, on lead 100. Thesepilot symbols are applied to the transmit antenna (Ant 1) via multiplexcircuit 118 and switch SW0 134 as previously described. The OTD encoder102 simultaneously produces pilot symbols B₁, S₁, −B₂ and −S₂ at symboltimes T-4T, respectively, at lead 104 for the OTD diversity antenna (Ant2). The pilot symbol pattern for the transmit and OTD diversity antennasis shown at TABLE I for the sixteen time slots of a frame. Each symbolincludes two bits representing a real and imaginary component. Anasterisk indicates a complex conjugate operation or sign change of theimaginary part of the symbol. Pilot symbol values for the first timeslot for the transmit antenna at lead 104, therefore, are 11, 11, 11 and11. Corresponding pilot symbols for the second antenna at lead 104 are11, 11, 00 and 00.

The bit signals r_(j)(i+τ_(j)) of these symbols are transmitted seriallyalong respective paths 208 and 210. Each bit signal of a respectivesymbol is subsequently received at a remote mobile antenna 212 after atransmit time τ corresponding to the j^(th) path. The signals propagateto a despreader circuit (FIG. 6) where they are summed over eachrespective symbol time to produce input signals R_(j) ¹, R_(j) ², R_(j)³ and R_(j) ⁴ corresponding to the four pilot symbol time slots and thej^(th) of L multiple signal paths.

The input signals corresponding to the pilot symbols for each time slotare given in equations [1-4]. Noise terms are omitted for simplicity.Received signals R_(j) ¹, R_(j) ², R_(j) ³ and R_(j) ⁴ are produced byrespective pilot symbols B₁, S₁, B₂ and S₂. Average channel estimates{circumflex over (α)}_(j) ¹ and {circumflex over (α)}_(j) ² over thefour pilot symbols for each antenna are obtained from a product of eachreceived signal and a complex conjugate of its respective pilot symbolas in equations [5] and [6].R _(j) ¹=(α_(j) ¹+α_(j) ²)B ₁  [1]R _(j) ²=(α_(j) ¹+α_(j) ²)S ₁  [2]R _(j) ³=(α_(j) ¹−α_(j) ²)B ₂  [3]R _(j) ⁴=(α_(j) ¹−α_(j) ²)S ₂  [4]{circumflex over (α)}_(j) ¹=(B ₁ *R _(j) ¹ +S ₁ *R _(j) ² +B ₂ *R _(j) ³+S ₂ *R _(j) ⁴)/4  [5]{circumflex over (α)}_(j) ²=(B ₁ *R _(j) ¹ +S ₁ *R _(j) ² −B ₂ *R _(j) ³−S ₂ *R _(j) ⁴)/4  [6]

Referring now to FIG. 4, there is a simplified diagram of a mobilecommunication system of the prior art. The mobile communication systemincludes an antenna 400 for transmitting and receiving external signals.The diplexer 402 controls the transmit and receive function of theantenna. Multiple fingers of rake combiner circuit 404 combine receivedsignals from multiple paths. Symbols from the rake combiner circuit 404,including pilot symbol signals, are applied to a bit error rate (BER)circuit 410 and to a Viterbi decoder 406. Decoded symbols from theViterbi decoder are applied to a frame error rate (FER) circuit 408.Averaging circuit 412 produces one of a FER and BER. This selected errorrate is compared to a corresponding target error rate from referencecircuit 414 by comparator circuit 416. The compared result is applied tobias circuit 420 via circuit 418 for generating a signal-to-interferenceratio (SIR) reference signal on lead 424.

Pilot symbols from the rake combiner 404 are applied to the SIRmeasurement circuit 432. The SIR measurement circuit produces a receivedsignal strength indicator (RSSI) estimate from an average of receivedpilot symbols. The SIR measurement circuit also produces an interferencesignal strength indicator (ISSI) estimate from an average ofinterference signals from base stations and other mobile systems overmany time slots. The SIR measurement circuit produces an SIR estimatefrom a ratio of the RSSI signal to the ISSI signal. This SIR estimate iscompared with a target SIR by circuit 426. This comparison result isapplied to TPC command circuit 430 via circuit 428. The TPC commandcircuit 430 sets a TPC symbol control signal that is transmitted to aremote base station. This TPC symbol instructs the base station toeither increase or decrease transmit power by 1 dB for subsequenttransmission.

Turning now to FIG. 5, there is a diagram showing a weighted multi-slotaveraging (WMSA) circuit 732 of the prior art for channel estimation. Inoperation, a signal buffer circuit 706 (FIG. 7) receives individualframes of data having a predetermined time period of 10 milliseconds.Each frame of the PCCPCH is subdivided into sixteen equal time slots of0.625 milliseconds each. Each time slot, for example time slot 528,includes a respective set of pilot symbols 520 and data symbols 529. TheWMSA circuit (FIG. 5) samples pilot symbols from preferably 6 time slotsfor a Doppler frequency of less than 80 Hz and from preferably 4 timeslots for a Doppler frequency of 80 Hz or more. These sampled pilotsymbols are multiplied by respective weighting coefficients α₁, throughα_(N) and combined by circuit 526 to produce a channel estimate. Thischannel estimate is used to correct the phase of received data symbolsin time slot 527 estimate for a respective transmit antenna.

Referring now to FIG. 6, there is a despreader circuit of the prior art.Received signals from mobile antenna 212 propagate to the despreadercircuit where they are summed over each respective symbol time toproduce output signals R_(j) ¹ and R_(j) ² corresponding to the j^(th)of L multiple signal paths as previously described. The despreadercircuit receives the i^(th) of N chip signals per symbol together withnoise along the j^(th) of L multiple signal paths at a time τ_(j) aftertransmission. Both here and in the following text, noise terms areomitted for simplicity. This received signal r_(j)(i+τ_(j)) at lead 600is multiplied by a channel orthogonal code signal C_(m)(i+τ_(j)) at lead604 that is unique to the receiver. Each chip signal is summed over arespective symbol time by circuit 608 and produced as first and secondoutput signals R_(j) ¹ and R_(j) ² on leads 612 and 614 as in equations[1-2], respectively. Delay circuit 610 provides a one-symbol delay T sothat the output signals are produced simultaneously.

This arrangement advantageously provides additional gain at the mobilecommunication system by multiple path transmit antenna diversity from aremote base station. The mobile unit, however, must be compatible withbase stations having a single transmit antenna as well as base stationshaving transmit antenna diversity. A problem arises, therefore, when themobile communication system is initially powered up or when it passesfrom one cell to another cell. The mobile unit must not only determinewhich of several base signals offers a preferable signal strength. Itmust also determine whether the base station offers transmit antennadiversity. If the mobile unit incorrectly decodes a received signal andassumes no transmit diversity, it loses the improved gain of transmitdiversity. Alternatively, if the mobile unit incorrectly decodes areceived signal and assumes transmit diversity, multiple fingers of therake combiner circuit 404 contribute noise to the received signal.

SUMMARY OF THE INVENTION

The foregoing problems are resolved by a circuit designed with ameasurement circuit coupled to receive an input signal from at least oneof a first antenna and a second antenna of a transmitter. Themeasurement circuit produces an output signal corresponding to amagnitude of the input signal. A control circuit is coupled to receivethe output signal, a first reference signal and a second referencesignal. The control circuit is arranged to produce a control signal inresponse to a comparison of the output signal, the first referencesignal and the second reference signal.

The present invention detects a diversity transmit antenna. A controlsignal modifies receiver signal processing to correspond to the presenceor absence of the diversity transmit antenna.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be gained by readingthe subsequent detailed description with reference to the drawingswherein:

FIG. 1 is a simplified block diagram of a typical transmitter of theprior art using OTD encoded pilot symbols and STTD encoded data symbolsfor the PCCPCH;

FIG. 2 is a block diagram showing signal flow of pilot symbol encodingin the OTD encoder of the transmitter of FIG. 1;

FIG. 3 is a diagram of pilot, data and search channel symbols of aPCCPCH time slot;

FIG. 4 is a simplified block diagram of a receiver of the prior art;

FIG. 5 is a block diagram showing weighted multi-slot averaging (WMSA)of the prior art;

FIG. 6 is a schematic diagram of a despreader circuit of the prior art.

FIG. 7A is a block diagram of a transmit diversity detection circuit ofthe present invention;

FIG. 7B is a block diagram of another embodiment of a transmit diversitydetection circuit of the present invention;

FIG. 7C is a block diagram of the measurement circuit 746 of FIG. 7A;

FIG. 8A is a simulation showing cumulative probability of detecting thepresence of transmit diversity as a function of time for the embodimentof FIG. 7A;

FIG. 8B is a simulation showing cumulative probability of not detectingtransmit diversity when present for the embodiment of FIG. 7A;

FIG. 9A is a simulation showing cumulative probability of detecting theabsence of transmit diversity as a function of time for the embodimentof FIG. 7A;

FIG. 9B is a simulation showing cumulative probability of detectingtransmit diversity when absent;

FIG. 10A is a simulation comparing normal and STTD decoding of singleantenna transmission for a Doppler frequency of 5 Hz with weightedmulti-slot averaging (WMSA); and

FIG. 10B is a simulation comparing normal and STTD decoding of singleantenna transmission for a Doppler frequency of 200 Hz with weightedmulti-slot averaging (WMSA).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 7A, there is a first embodiment of a mobile unitof the present invention configured for blind detection of transmitdiversity. This blind detection scheme includes a new implementation ofan algorithm disclosed by A. Wald, Sequential Analysis (1947). Mobileantenna 212 receives multipath signals transmitted by base stationantennas at leads 180 and 182 (FIG. 1), respectively. Diplexer circuit702 couples these received multipath signals to lead 704 during receivemode operation. Doppler frequency estimator circuit 740 is described indetail in copending U.S. patent application Ser. No. 09/224,632, filedDec. 31, 1998, and incorporated herein by reference. Doppler frequencyestimator circuit 740 receives the multipath signals on lead 704 andproduces an output signal on lead 742 corresponding to the estimatedDoppler frequency. Delay profile estimator circuit 720 also receives themultipath signals on lead 704. Delay profile estimator circuit 720includes a despreader circuit as in FIG. 6 and a match filter circuit(not shown). The delay profile estimator circuit 720 determines which ofthe received multipath signals should be combined based on the strengthof the matched filter output.

Operation of the measurement circuit 746 will now be explained in detailwith reference to FIG. 7C. The measurement circuit 746 receives pilotsymbol data from received multipath signals on lead 704. Channelestimate circuit 750 generates separate diversity signals X₁ and X₂,corresponding to antennas on leads 180 and 182, respectively. Theseseparate diversity signals include pilot symbols from a series of timeslots. Coherent averaging circuit 756 coherently averages the energy ofall received pilot symbol data from the respective antennas at leads 180and 182 from K time slots in response to the Doppler frequency estimatorcircuit output signal on lead 742 and produces signals {tilde over (X)}₁and {tilde over (X)}₁ on respective leads 758 and 760. The variable K ispreferably the same number of time slots used by the WMSA circuit ofFIG. 5. It is preferably equal to six time slots for Doppler frequenciesbelow 80 Hz and preferably equal to four time slots for Dopplerfrequencies of 80 Hz or more. Non-coherent averaging circuit 762 thennon-coherently averages the signals {tilde over (X)}₁ and {tilde over(X)}₁ over the respective multipaths and produces signals |{tilde over(X)}₁| and |{tilde over (X)}₂| at leads 764 and 766, respectively, inresponse to the output signal on lead 744 from the delay profileestimator circuit. Ratio circuit 768 produces an output signal λ at lead722 that is a ratio of the signals |{tilde over (X)}₁| and |{tilde over(X)}₂| from the primary antenna at lead 180 and the diversity antenna atlead 182, respectively.

Comparator circuit 726 compares the output signal λ at lead 722 to thefirst reference signal η₁ and the second reference signal η₂ at leads723 and 724, respectively. These reference signals are programmed suchthat reference signal η₁ is greater than reference signal η₂. Whenoutput signal λ is greater than reference signal η₁, the comparatorcircuit produces a control signal on lead 728 indicating no transmitdiversity. This control signal is applied to WMSA channel estimatecircuit 732. The WMSA channel estimate circuit sets the channel estimateα_(j) ² at lead 736 to zero, thereby eliminating any noise contributionto the received signal. Phase correction circuit 710 then applies thechannel estimate α_(j) ¹ at lead 734 to the received signal at lead 708from signal buffer 706. The phase correction circuit applies a correctedreceived signal from the primary antenna at lead 180 to rake combinercircuit 712. This rake combiner circuit then combines correctedmulti-path signals from the primary antenna and applies the resultingcombined signal to Viterbi decoder circuit 714. The Viterbi decoderproduces a received signal at lead 716.

Alternatively, when output signal λ is less than reference signal η₂,the ratio of signals from the primary and diversity antennas is nearunity. The comparator circuit 726, therefore, produces a control signalon lead 728 indicating transmit diversity. The control signal is alsoapplied to WMSA channel estimate circuit 732. The WMSA channel estimatecircuit responsively produces channel estimate signals α_(j) ¹ and α_(j)² at leads 734 and 736, respectively. Phase correction circuit 710 thenapplies both channel estimates to the received signal at lead 708 fromsignal buffer 706. The phase correction circuit then applies correctedsignals from the primary antenna at lead 180 and the diversity antennaat lead 182 to rake combiner circuit 712. This rake combiner circuitthen combines corrected multi-path signals from both antennas andapplies the resulting combined signal to Viterbi decoder circuit 714.The Viterbi decoder produces a received signal at lead 716.

When output signal λ is less than reference signal η₁ but greater η₂,the ratio of signals is indeterminate and comparator circuit 726 doesnot change the control signal on lead 728. Thus, WMSA channel estimatecircuit continues to produce channel estimates corresponding to theprevious state. Likewise, phase correction circuit 710, rake combiner712 and Viterbi decoder 714 continue in the same mode of operation untiloutput signal λ exceeds the bounds of one of the reference signals,thereby indicating an unambiguous presence or absence of diversity.Furthermore, reference signal η₁ and η₂ preferably converge to a singlevalue η over time. This sequential convergence assures sequentialdetection of diversity or non-diversity over time.

The simulation output of FIG. 8A shows cumulative probability ofdetecting the presence of transmit diversity as a function of time forthe embodiment of FIG. 7A. The simulation conditions include 40 trafficchannels, each having a gain equal to the PCCPCH. Reference signals η₁and η₂ converge to η linearly over 48 frames for Doppler rates of 5 Hzand 20 Hz and over 24 frames for a vehicular Doppler rate of 200 Hz. Thesimulation shows 99% cumulative probability of detection of a diversityantenna at 250 milliseconds, 145 milliseconds and 30 milliseconds forDoppler frequencies of 5 Hz, 20 Hz and 200 Hz, respectively. Thesimulation of FIG. 8B shows cumulative probability P_(m) of notdetecting transmit diversity when present for the embodiment of FIG. 7A.The simulated probabilities are 1.7×10⁻³ and 1.2×10⁻⁴ for pedestrianDoppler frequencies of 5 Hz and 20 Hz, respectively. No error occurredat a 200 Hz Doppler frequency.

The simulation output of FIG. 9A shows cumulative probability ofdetecting the absence of transmit diversity as a function of time forthe embodiment of FIG. 7A. Under the same simulation conditions as FIG.8, the simulation shows 99% cumulative probability of detecting theabsence of a diversity antenna at 170 milliseconds, 140 milliseconds and55 milliseconds for Doppler frequencies of 5 Hz, 20 Hz and 200 Hz,respectively. The simulation of FIG. 9B shows cumulative probabilityP_(f) of detecting transmit diversity when not present for theembodiment of FIG. 7A. The simulated probabilities are 6.5×10⁻³,3.6×10⁻³ and 6.1×10⁻⁴ for Doppler frequencies of 5 Hz, 20 Hz and 200 Hz,respectively. No error occurred at a 200 Hz Doppler frequency.

The blind detection circuit of FIG. 7A, therefore, reliably detects thepresence of transmit diversity in less than 250 milliseconds. Moreover,the probability of missing P_(m) an active diversity antenna is lessthan 1.7×10⁻³, and the probability of false detection P_(f) of an absenttransmit diversity antenna is less than 6.5×10⁻³. This method ofdetection is highly advantageous when time permits. No specialconsideration is required at the base station to accommodate mobiledetection. The mobile relies on a ratio of signals from the primary anddiversity antennas for detection. Thus, decoding of transmitted signalsis unnecessary for this method of blind detection.

Turning now to FIG. 7B, there is a second embodiment of a mobile unit ofthe present invention configured for Level 3 (L3) message detection oftransmit diversity. This L3 message is a QPSK-encoded binary messagethat is transmitted on the PCCPCH together with other information suchas whether the PCCPCH is STTD encoded, neighboring base stations,Secondary Common Control Physical Channel (SCCPCH) offset and basestation received power. The mobile unit applies received signals to thedelay profile estimator circuit 720 and signal buffer circuit 706 aspreviously described. The delay profile estimator circuit applies acontrol signal corresponding to the Doppler rate of the received signalto the WMSA channel estimate circuit 732 via lead 728. This controlsignal determines the variable K number of time slots used by the WMSAchannel estimate circuit 732 (FIG. 5). The mobile unit initially assumesthe received signal is STTD encoded and produces a correspondingdiversity control signal on lead 738. The diversity control signalenables production of channel estimate signals α_(j) ¹ and α_(j) ² atleads 734 and 736, respectively. Phase correction circuit 710 receivesthese channel estimate signals together with the data signals on lead708 and produces a phase-corrected signal at rake combiner circuit 710.If the received data signal is STTD-encoded, the rake combiner circuit712 combines multi-path data signals from the respective primary anddiversity antennas and applies them to Viterbi decoder circuit 714. TheViterbi decoder circuit 714 decodes the L3 message to determine if themessage contains information on STTD signal encoding of PCCPCH andproduces diversity control signal on lead 738. If the L3 messagecontains information that the original PCCPCH data was STTD-encoded,operation of the receiver continues as previously described. Thus, themobile unit with STTD realizes a typical 3 dB gain for a 5 Hz Dopplerfrequency corresponding to pedestrian indoor-to-outdoor transmission anda typical 0.6 dB gain for a 200 Hz Doppler frequency corresponding tovehicular transmission compared to non-diversity transmission.

When the L3 message includes information that the original PCCPCH datawas not STTD-encoded, however, the Viterbi decoder circuit 714 changesthe logic state of the control signal on lead 738. This non-diversitycontrol signal on lead 738 disables the diversity channel estimate α_(j)² on lead 736. The non-diversity control signal further disables thephase-corrected output from phase correction circuit 710, therebyeliminating noise at the rake combiner circuit 712 due to an absentdiversity signal.

The received L3 message is degraded at the mobile receiver when STTDsignal encoding is incorrectly assumed prior to initial decoding. Thisdegradation is due to noise at the rake combiner circuit fingerscorresponding to the absent diversity antenna. The degradation due tothis noise is shown at the simulated output of FIG. 10A. The simulationcompares normal and STTD signal decoding of single antenna transmissionfor a Doppler frequency of 5 Hz with weighted multi-slot averaging(WMSA). The received channel energy to noise ratio (E₀/N₀) increases byonly 0.2-0.4 dB for a selected bit error rate (BER). A comparable resultis evident from the simulation comparing normal and STTD signal decodingof single antenna transmission for a Doppler frequency of 200 Hz withWMSA (FIG. 10B). The received channel energy to noise ratio (E₀/N₀) forthis vehicular Doppler frequency of 200 Hz increases by 0.6-0.7 dB for aselected bit error rate (BER). A nominal degradation of the receivedchannel energy to noise ratio (E₀/N₀) of 0.2-0.7 dB at the mobile unitwill not inhibit correct demodulation of the L3 diversity message. Thismethod of diversity detection is highly advantageous in reducingdiversity detection time. The decoding of the information in the L3message affirmatively indicates the presence or absence of diversitytransmission at the output of the Viterbi decoder in less than 30milliseconds. Only nominal signal degradation occurs by incorrectlydecoding a non-diversity L3 message as though it were STTD signalencoded.

Although the invention has been described in detail with reference toits preferred embodiment, it is to be understood that this descriptionis by way of example only and is not to be construed in a limitingsense. For example, advantages of the present invention may be achievedby a digital signal processing circuit utilizing a combination ofhardware and software operations as will be appreciated by those ofordinary skill in the art having access to the instant specification.Furthermore, the advantages the blind detection method of signaldiversity detection of FIG. 7A and the L3 message diversity detection ofFIG. 7B may be combined. For example, the mobile unit may initially usethe blind detection method to determine a presence or absence oftransmit diversity. The result of this determination may then be used todecode the L3 message from the base station. The decoded L3 message maythen be used to confirm the blind detection result. When results differ,however, the process may be repeated. In another embodiment of thepresent invention, the mobile unit may use either blind detection or L3message decoding to determine a presence or absence of transmitdiversity among neighboring base stations as well as a selected basestation. In yet another embodiment of the present invention the mobileunit may receive transmit diversity information together with long codegroup information about neighboring base stations from the selected basestation via L3 message decoding.

1. A process of detecting transmit diversity comprising: A. receiving adiversity encoded signal from a base station at an antenna of a mobileunit, the receiving occurring on a primary common control physicalchannel, and the signal carrying a message of information; and B.decoding the message carried by the received signal to determinetransmit diversity signal encoding information contained in the message;C. the receiving including receiving a diversity encoded Level 3 messagesignal, and including: producing a first control signal corresponding tothe Doppler rate of the received Level 3 message signal; producing twochannel estimate signals in response to the first control signal and adiversity control signal indicating STTD diversity; enablingphase-correction of the Level 3 message signal by the two channelestimate signals in response to the diversity control signal; rakecombining multipath data signals from the Level 3 message signal and thetwo channel estimate signals in response to the diversity controlsignal; and decoding the rake combined Level 3 message and producing theSTTD diversity control signal indicating STTD diversity.
 2. The processof claim 1 in which the decoding includes decoding information onneighboring base stations, secondary common control physical channeloffset, and base station received power.
 3. A process of detectingtransmit diversity information contained in a Level 3 message,comprising: receiving a Level 3 message signal at an antenna of a mobileunit; producing a first control signal corresponding to the Doppler rateof the received Level 3 message signal; producing two channel estimatesignals in response to the first control signal and a diversity controlsignal indicating STTD diversity, and one channel estimate signal inresponse to the first control signal and the diversity control signalindicating no STTD diversity; enabling phase-correction of the Level 3message signal by the two channel estimate signals in response to thediversity control signal indicating STTD diversity and disabling thephase-correction of the Level 3 message signal in response to thediversity control signal indicating no STTD diversity; rake combiningmultipath data signals from the Level 3 message signal and the twochannel estimate signals in response to the diversity control signalindicating STTD diversity, and from the Level 3 message and the onechannel estimate signal in response to the diversity control signalindicating no STTD diversity; and decoding the rake combined Level 3message and producing one of the diversity control signal indicatingSTTD diversity and the diversity control signal indicating no STTDdiversity.